Electrostatically actuated oscillating structure with oscillation starting phase control, and manufacturing and driving method thereof

Patent metadata

Field	Value
Publication number	US-9753279-B2
Application number	US-201414564237-A
Country	US
Kind code	B2
Filing date	Dec 9, 2014
Priority date	Dec 12, 2013
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

An electrostatically actuated oscillating structure includes a first stator subregion, a second stator subregion, a first rotor subregion and a second rotor subregion. Torsional elastic elements mounted to the first and second rotor subregions define an axis of rotation. A mobile element is coupled to the torsional elastic elements. The stator subregions are electrostatically coupled to respective regions of actuation on the mobile element. The stator subregions exhibit an element of structural asymmetry such that the electrostatic coupling surface between the first stator subregion and the first actuation region differs from the electrostatic coupling surface between the second stator subregion and the second actuation region.

First claim

What is claimed is:

1. An electrostatically actuated oscillating structure, comprising:
a fixed support body forming a first stator subregion, a second stator subregion, a first rotor subregion and a second rotor subregion;
a first torsional elastic element and a second torsional elastic element mechanically coupled, respectively, to the first and second rotor subregions and defining an axis of rotation parallel to a first direction of an orthogonal reference system; and
a mobile element arranged between, and connected to, said first and second torsional elastic elements, the mobile element being rotatable about the axis of rotation as a result of a torsion of the first and second torsional elastic elements;
wherein the first and second stator subregions are electrostatically coupled to respective first and second regions of actuation of the mobile element, which are diametrically opposite to one another with respect to the axis of rotation,
wherein one of the first and second stator subregions includes at least an element of structural asymmetry such that a surface available for said electrostatic coupling between the first stator subregion and the first actuation region is greater than a surface available for the electrostatic coupling between the second stator subregion and the second actuation region;
wherein said element of structural asymmetry is a bump element of increased thickness housed by the first stator subregion such as to increase a spatial extension, in a second direction orthogonal to said first direction, of a portion of the first stator subregion with respect to a spatial extension in said second direction of a corresponding portion of the second stator subregion;
wherein the first and second regions of actuation of the mobile element include a respective plurality of first and second elongated elements, which extend in cantilever fashion towards the first and second stator subregions, respectively, the first and second stator subregions including a respective plurality of third and fourth elongated elements comb-fingered to the first and second elongated elements, respectively; and
wherein said bump element of increased thickness extending, at least in part, on the third elongated elements, so that the surface available for said electrostatic coupling between the third elongated elements and the first elongated elements is greater than the surface available for the electrostatic coupling between the fourth elongated elements and the second elongated elements.

2. The oscillating structure according to claim 1 , wherein said spatial extension of said bump element is of a value greater than a threshold, said threshold being the maximum value of manufacturing error to which the oscillating structure may be subject during manufacturing thereof.

3. The oscillating structure according to claim 1 , wherein the first stator subregion comprises a main body extending from which in cantilever fashion are said third elongated elements, said bump element of increased thickness further extending in an area corresponding to a surface region, contiguous to the third elongated elements, of the main body of the first stator subregion.

4. The oscillating structure according to claim 1 , further comprising an electronic circuit operatively coupled to the first and second stator subregions and to the mobile element, configured to bias the mobile element at a reference voltage and for biasing the first and second stator subregions by an electrical driving signal including a train of pulses having a voltage value greater, in modulus, than the reference voltage, and such as to generate, and maintain, an oscillation of the mobile element.

5. The oscillating structure according to claim 4 , wherein each between said first and second torsional elastic elements has a first dimension, a second dimension, and a third dimension, measured respectively in a first direction, a second direction, and a third direction, orthogonal to one another, said first dimension being greater than said second and third dimensions, said first and second stator subregions being arranged in such a way that, when they receive the electrical driving signal, the mobile element rotates about the axis of rotation parallel to the first direction.

6. The oscillating structure according to claim 1 , wherein the fixed support body, the first and second torsional elastic elements, and the mobile element are made of semiconductor material.

7. A method, comprising:
(a) shaping a fixed support body to form a first stator subregion and a second stator subregion and a first rotor subregion and a second rotor subregion;
(b) forming a first torsional elastic element and a second torsional elastic element, constrained, respectively, to the first and second rotor subregions and defining an axis of rotation;
(c) forming a mobile element set between, and connected to, said first and second torsional elastic elements, the mobile element being rotatable about the axis of rotation as a result of a torsion of the first and second torsional elastic elements; and
(d) forming first and second regions of actuation of the mobile element, which are diametrically opposite to one another with respect to the axis of rotation;
wherein steps (c) and (d) include electrostatically coupling the first and second stator subregions to the first actuation region and to the second actuation region, respectively,
(e) forming, in an area corresponding to one between the first and second stator subregions, an element of structural asymmetry such that a surface available for said electrostatic coupling between the first stator subregion and the first actuation region is greater than a surface available for the electrostatic coupling between the second stator subregion and the second actuation region;
wherein the step of forming said element of structural asymmetry includes forming a bump element of increased thickness in a portion of the first stator subregion, for increasing at least in part a spatial extension, in a second direction orthogonal to said axis of rotation, of the first stator subregion with respect to a spatial extension, in the second direction of a corresponding portion of the second stator subregion;
wherein step (d) includes forming a respective plurality of first and second elongated elements, which extend in cantilever fashion towards the first and second stator subregions, respectively; and
wherein step (c) includes forming a respective plurality of third and fourth elongated elements comb-fingered to the first and second elongated elements, respectively; and
wherein step (e) includes forming said bump element so that the surface available for said electrostatic coupling between the third elongated elements and the first elongated elements is greater than a surface available for the electrostatic coupling between the fourth elongated elements and the second elongated elements.

8. The method according to claim 7 , wherein the step of forming the bump element includes forming the bump element having a spatial extension, in a second direction orthogonal to said first direction, of a value greater than a threshold, said threshold being the maximum value of fabrication error to which the oscillating structure is subj ect during manufacturing thereof.

9. The method according to claim 7 , wherein the first stator subregion comprises a main body, said fourth elongated elements being formed so as extend in cantilever fashion from the main body, the step of forming the bump element further including forming the bump element of increased thickness in an area corresponding to a surface region of the main body of the first stator subregion, contiguous to the third elongated elements.

Assignees

• St Microelectronics Srl
• St Microelectronics Int Nv

Inventors

• Vigna Benedetto
• Ferrera Marco
• Costantini Sonia
• Salina Marco

Classifications

• B81B2201/042

  Micromirrors, not used as optical switches · CPC title

• G02B26/0841 Primary

  the reflecting element being moved or deformed by electrostatic means · CPC title

• H04N9/3129

  scanning a light beam on the display screen (scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161) · CPC title

• H04N9/3135

  Driving therefor · CPC title

• H02N1/006

  of the gap-closing type (H02N1/004 takes precedence) · CPC title